Screens are often used in high erosion industrial environments where it is desirable to separate particulates from a fluid in which the particulates are entrained. The screens are typically in the form of grates, perforated plates or woven mesh. For example, steel screens are used in coal-fired power plants to capture and separate coarse fly ash particles from hot gas streams. Conventional screens subjected to such high erosion environments exhibit significant wear and must be replaced or repaired frequently, resulting in lost productivity while the worn screens are removed from operation.
Published U.S. Patent Application No. US 2006/0210721 A1 to Hall discloses thermal spray processes for coating metal screens in which multiple spray heads direct coating materials onto the screen from different angles. Although the thermally sprayed coatings of Hall '721 are said to increase wear resistance of the screens, they suffer from problems such as excessive waste of the wear resistant material.
U.S. Pat. No. 6,649,682 B1 to Breton et al., which is incorporated herein by reference, discloses a paint system and process for hardfacing metal surfaces such as fan blades, pipes, pumps and valves. In the '682 Brenton et al. patent, a paint that includes a dispersion of hard particles is first applied as a coating to the surface of the substrate. Next, a paint including a dispersion of braze alloy is applied over the layer of hard particles. The substrate is then heated to cause the braze alloy to melt and infiltrate into the hard particles thereby bonding them to the metallic surface. The '682 Brenton et al. patent also discloses an embodiment of the process wherein a first layer of adhesive is applied to the substrate and a hardfacing powder is then applied to the adhesive. A second layer of adhesive is applied and a braze alloy powder is applied to the second adhesive. The substrate is then heated whereby the braze alloy melts and infiltrates into the hard particles so as to bond them to the metallic surface. In a third embodiment of the '682 Breton et al. patent, a hardfacing alloy powder containing precipitated intermetallic hard compounds is made into a paint and applied to the surface that is to be protected. After drying, the paint is heated to form a coating. In a fourth embodiment, hardfacing particles and braze alloy powder are made into a paint and applied to the surface to be protected. The paint is then dried and heated to form the coating.
In a process such as that disclosed in '682 Breton et al. patent, in order to obtain a layer of the paint that includes a dispersion of hard materials that has sufficient thickness, it takes multiple coats (or dips) of the substrate into the paint to achieve the necessary cladding thickness. At sharp corners or edges of the substrate the paint has a tendency to pull away which results in a thinner cladding and a premature wear in these areas adjacent to the sharp corners or edges of the substrate.
It would be desirable to provide a coating process which produces a highly effective wear-resistant coating on an article, such as a screen.
It would also be desirable to provide an article, such as a screen, with a wear-resistant coating which significantly increases wear resistance of the article when subjected to high erosion environments.